Note:You can remove individual website cookies in Firefox version 60 and below, using the Page Info windowSecurity tab View Cookies button. You can also use the Storage Inspector to remove individual cookies for a specific website, via the right-click context menu. To open the Storage Inspector, go to the menu button
Web Developer submenu or press Shift + F9 on the keyboard.

Delete all cookies

To delete all cookies stored on your computer, either open the Cookies window as explained above and use the Remove All Cookies button,either go to your Cookies and Site Data settings as explained above, click Clear Data… and then click Clear to remove all cookies and site data or else do the following:

Click the menu button
and click Library (or click the Library button
in the toolbar).

Click History and then click Clear Recent History….

Set Time range to clear to Everything.

Click on the arrow next to Details to expand the list of history items.

Select Cookies and make sure that other items you want to keep are not selected.

Click Clear Now to clear the cookies and close the Clear Recent History window.

Click the menu button
, choose History and then Clear Recent History….

Set Time range to clear to Everything.

Click on the arrow next to Details to expand the list of history items.

Select Cookies and make sure that other items you want to keep are not selected.

Click Clear Now to clear the cookies and close the Clear Recent History window.